Respiratory disease is a major cause of human death, SO2 a ubiquitous urban air pollutant. The nose is the first site of impact of respiratory viruses and toxins, epithelial sloughing its primary response, mucosal regeneration a necessary result. Combined effects of virus and SO2 on nasal membranes have not been studied. We will study interactions of acute NDV infection and SO2, and of chronic laryngotracheitis plus SO2. NDV sharply depresses, SO2 greatly increases cell multiplication during the first week of exposure, and acute NDV and LTV soften and distort underlying cartilage (our data). Established methods virology, histopathology, histochemistry, autoradiography, fluorescent antibody will be used to study virus-SO2 interactions on: virus absorption, pathogenesis, spread to lower tract; cell kinetics; chronicity and neoplasia; and cartilage integrity.